Brief Description of the Prior Art
A number of machines have previously been provided which can be utilized to make a trench or furrow in the earth, and concurrently lay within that trench a cable, flexible pipe or the like. Generally these devices utilize a self-propelled vehicle, such as a tractor, and provide a plow or blade which is pulled through the earth by the tractor to open the trench which is to receive a cable or flexible pipe. The cable or pipe is fed into the trench through a suitable guide mechanism, frequently from a reel mounted at an elevated location on the apparatus. In some systems, this feeding of the cable or flexible pipe is accomplished manually, and in some instances, it is fed off of the reel or source of supply by a powered constant speed feed motor.
It is known to provide, as an aid to the trench or furrowforming part of the cable burying operation, a vibration developing structure by which an oscillating up-and-down motion is periodically developed. The cyclically occurring up-and-down forces thus periodically developed are transmitted through intervening structure to the plow blade. This enhances the progression of the plow blade through the soil in that it imparts a periodic impact force component to the plow which aids its advance.
In some other types of vibratory plows, periodically acting opposed force vectors are developed which act in directions other than up-and-down.
In U.S. Pat. No. 3,405,533 issued on Oct. 15, 1968 to Fries, two cable burying plow structures of the type described are illustrated. In one of these, a vibrating frame is provided and is attached to a tractor or other pulling vehicle. A plow shank 30 is mounted on the vibrating frame so that the oscillatory and periodic vibrations are imparted to the shank. The plow shank 30 is provided with connecting structures enabling it to support a cable guide carried behind the plow shank, and functioning to guide a cable over a series of sheaves or pulleys to a substantially horizontal path aligned with the lower edge of the plow blade and shank so that the cable is laid in the trench or furrow formed by the vibrating plow blade as it is pulled through the earth by the tractor.
A second form of the cable laying assembly is also shown in this patent. In this apparatus, the cable is fed principally through an elongated tube which extends transversely across the shank of the plow and into a position of horizontal alignment with the point of the plow so as to discharge the cable guided through the tube into a trench or furrow formed by the plow.
A cable laying system is depicted and described in U.S. Pat. No. 3,788,575. In that system, the large reel upon which the cable is stored, and from which it is paid out as it is placed in a trench by the apparatus, is positively driven by a hydraulic motor. This assures that the anchoring tension developed in the cable as it is placed in the trench and then covered does not part the cable due to inertial forces in the reel. The hydraulic motor is responsive to the tension in the cable to speed up or slow down the reel as may be needed.
The apparatus by which the cable is placed in a trench in U.S. Pat. No. 3,788,575 includes an elongated tubular element functioning as a cable guide, and carried behind an elongated, point-carrying conventional trencher which forms the narrow trench into which the cable is deposited. This entire assembly is carried on the back of a cable laying framework which is mounted on road wheels, and is adapted to be towed in a conventional manner behind a traction unit. U.S. Pat. No. 3,788,575 also points out how, in some instances prior to the time of the patent, cables had been manually paid out from the reel as the demands of the span of cable deposited in the trench required. This patent also points out that in some prior art forms of cable laying devices, the cable had been positively driven through the cable guide for deposition in the trench by frictional drive elements which positively engaged the cable itself.
One method of frictionally advancing a cable or tubular element in incremental movements is disclosed in U.S. Pat. No. 2,912,100. In this patent, a quick acting drive mechanism is provided which acts through an eccentric cam drive to periodically drive a rack which engages a gear wheel forming a part of a pawl and ratchet arrangement. The gear wheel is keyed to a drive roller acting as one of two rollers through which a cable is passed. At periodic intervals, the drive roller is rotated through an increment of rotation to effectively drive the cable in a corresponding increment of advance.
Another apparatus by which a cable or wire can be incrementally advanced in selected intervals during rotation of a cable-engaging pair of rollers is disclosed in U.S. Pat. No. 2,904,167. In this system, a drive motor acts as a linkage to periodically cause arms carrying dogs to oscillate so as to engage a ratchet wheel having selectively spaced teeth thereon. The ratchet wheel thus is caused to also undergo an intermittent angular advance as the teeth are engaged and released by the dog carried on the oscillating linkage. The ratchet wheel in turn drives a drive roller which is one of a pair of rollers through which the cable is extended, and by which it is frictionally engaged. Slippage of the rollers on the cable can be eliminated, or it may be allowed to occur in a controlled measure as the rollers drive the cable.
Yet another cable or conduit placing machine is shown in Hash U.S. Pat. No. 2,722,181.
An interesting arrangement for driving the cable through a cable guide tube to a location in the bottom of the trench is illustrated in Ryan U.S. Pat. No. 3,066,491. In the Ryan patent, a hand guided cable or wire laying apparatus is depicted. This apparatus basically includes a frame pulled behind a powered vehicle, and supported on ground-engaging wheels. The axle which interconnects the ground-engaging wheels carries a sprocket which drives a chain extending rearwardly along the frame until it comes to a location over the cable guide tube where the cable is passed into the upper end of the cable guide tube. At this location, the sprocket driven chain continuously drives a pair of force feed rollers which engage the cable, and force it into the upper end of the cable guide tube. The drive is continuous, of course, rather than intermittent, and the rate of feed is controlled by the rate at which the powered chain is driven by the ground-engaging wheels. Adjusting means is provided to adjust the amount of clearance between the force feed rollers which engage opposite sides of the cable for driving it downwardly through the cable tube. Thus, the size of cable so driven can be varied, as well as degree of slippage of the rollers against the cable.
In Davis U.S. Pat. No. 3,363,423, an underground cable laying implement is illustrated and described. In the Davis machine, the trench slitting blade generally characteristic of this type of apparatus is provided, and is trailed by a cable guide tube through which the cable is fed into the trench formed by the blade. The guide tube is made to float, or to be pivotable on the blade, so that a reciprocating motion imparted to the blade by a blade reciprocating mechanism is not transferred to the cable guide tube.
The blade reciprocating mechanism employed includes a housing mounted on the blade-carrying frame, and within this housing, a pair of counterrotating wheels or gears is supported. These wheels rotate in opposite directions, and carry a pair of corresponding eccentric weights located near the outer periphery of the gears, and rotated with them in counterrotative directions. The synchronization of movement and location of the eccentric weights is such that additive upward components of force, and additive downward components of force are periodically developed as the gears or wheels are counterrotated and the eccentric weights act in an additive fashion to produce the upward components and downward components of force. This causes the blade to reciprocate up and down. Concurrently, of course, it is being pulled forward by the vehicle upon which the cable laying implement is mounted.
In U.S. Pat. No. 3,713,300, a manually guided cable laying device includes front and rear traction wheels which are located on the opposite sides of a vertical line in which the digger blade is located. The digger blade is caused to undergo both a forward movement and an oscillatory motion which causes it to move through an eliptical path. The digger blade, by reason of this motion, meters or pulls cable through a cable guide disposed between the pair of traction wheels.
Another type of vibratory cable laying plow which is currently marketed is a cable laying vibratory plow manufactured by The Charles Machine Works of Perry, Okla. This company makes several types of vibratory cable laying plows, but one, referred to as a VP75, uses counterrotating, eccentric weight-carrying discs or plates to impart a vibratory motion to the plow blade as it is pulled through the earth. A pair of gauge skids set the depth at which the plow blade will penetrate into the earth. A cable feed tube is secured to the rear side of the plow blade, and functions to feed a cable into the narrow trench formed by the vibrating plow.